(1) Field of the Invention
The invention relates to the field of building up land in water-covered or water-surrounded areas and more specifically to the field of restoring land in coastal wetlands where erosion has caused land loss. This invention also relates to the field of building land bodies in water-covered or water-surrounded areas.
(2) Description of the Related Art
Coastal wetlands historically have been rich in plant and animal life. This abundance of plant and animal life has made coastal wetlands productive areas for fishing (for fish and shellfish), trapping, and hunting.
Coastal wetlands require a constant supply of sediment so that the process of sedimentation keeps pace with erosion. In a coastal wetland, the land is built up by sedimentation and broken down by erosion. In a stable coastal wetland, these processes are in balance when considered over the long term: land loss through erosion and land gain from sedimentation remain essentially equal. Seasonal or unusual events such as floods or storms may cause erosion and sedimentation to become unbalanced for a time. But in a stable wetland, erosion and sedimentation remain in balance over the long term.
Over at least the last 100 years, human activities have affected the natural balance between erosion and sedimentation in many coastal wetlands. Levees and other developments have reduced the flow of fresh water into many coastal wetlands. These developments have reduced the amount of sedimentation in the affected coastal wetlands by eliminating the sediment flows that were carried by the fresh water flow.
In addition to reducing sedimentation, the reduction of fresh water flow has also promoted erosion. The reduction of fresh water flow has changed the chemical composition—especially the salinity—of water in some coastal wetlands. Plants adapted to the previous (lower) salinity levels often die when salinity increases. Killing the plants increases erosion because many plants hold the land together and help to absorb impacts of waves and other water flows. When the plants die, erosion increases.
With erosion increasing and sedimentation decreasing, land area in coastal wetlands has shrunk. Facing the loss of a valuable resource, public officials and citizens have sought ways to reduce erosion and increase sedimentation in coastal wetlands so that lost land may be restored. Fresh water diversion from rivers into coastal wetlands merely keeps salt water at bay and does little to promote land restoration, not only because of decreased sediment in leveed rivers but also because diversion of fresh water typically uses siphons or pipes that place sediment-containing water into a single location rather than over a broader plain. Rivers currently contain seventy percent less sediment than they did fifty years ago because of flood-prevention methods upstream.
Applicant's U.S. patent application Ser. No. 10/695,640, now U.S. Pat. No. 6,922,922 B2, and U.S. patent application Ser. No. 10/349,599, now U.S. Pat. No. 6,827,525 B2, disclose devices, systems, and methods for restoring wetlands and building up land using a cutterhead dredge and other devices.